Strobed approach lighting systems (sometimes known as the “rabbit”) are important features of the airfield environment, particularly in low visibility, as they extend many hundreds of feet into the approach path beyond the runway threshold. They are also the brightest elements of the approach lighting systems often found in an airport. The strobed approach lighting system gives signals to the pilots to permit (or bar) approach to the airport, particularly in low visibility conditions.
Pre-existing enhanced vision systems (“EVS”) and enhanced vision flight system (“EFVS”) systems cannot reliably detect the strobed portion of the approach lighting systems (the “rabbit”) as these systems are “blind” at regular time intervals due to internal electronic constraints—detector readout, limited integration time to prevent saturation, etc. For example, in high-brightness environments (e.g. sunlit fog) a sensor might only stare at the real world scene for 1 ms out of the perhaps 16 ms typical frame update time, in order to prevent saturation. The inability of pre-existing systems to detect strobes reliably has been cited by the Federal Aviation Administration (“FAA”) as a major drawback of current systems. Even when integration times are longer, a portion of the frame time is devoted to detector readout, and during this dead time the system is blind to the external scene and “misses” a subset of the strobe pulses. In addition, this temporal undersampling of the pulsed system causes misleading and erroneous rendering of the lights, sometimes making them appear as traveling in the wrong direction.